There are numerous kinds of electrochemical cells, the common element being that applying an electrical charge to such a cell causes a chemical change or change in the ionic structure of such a cell. Many types of electrochemical cells comprise electrodes and electrolyte, in which the chemical reaction between said chemicals is driven by discharging or charging said electrodes. Such a cell can be either a passive cell or a battery cell. In a passive cell, electricity needs to be introduced into the cell in order to “drive” the chemical reaction. In a battery cell or fuel cell, the cell itself generates electricity as the reaction runs, providing that a discharge circuit is provided. In the case of a passive cell (or a battery on charge), the rate of reaction is determined by the electrical power applied; whereas in a battery cell which is discharging, the control over the energy consumption determines the rate of discharge of the battery. The definition of battery cells herein includes not only conventional type batteries (using either “wet” or “dry” chemistry) but also (a) lithium “shuttle” type batteries in which the process is that ions in the electrolyte shuttle back and forth between the electrodes as opposed to participating in a conventional chemical reaction; and (b) sealed fuel cells in which a fixed starting amount of fuel is used up as the cell discharges. The present invention applies to all the above types of cell, providing only that the chemical process involved is such that it causes a volume change within the cell as the process proceeds.
In the field of battery cells, the volume change generated as the battery charges or discharges is a known yet undesirable side effect, said effect being mentioned in the prior art. For example, US Patent Application 20040115530 describes a method of preventing the detrimental effects of the volume change of the active material in a lead-acid battery cell. However, in the present invention, such “undesirable” volume changes are exploited in order to deliver a useful feature: precise, controlled drug-delivery such as that required for slow-infusion or implanted medical devices.
Numerous types of inexpensive drug-delivery mechanisms are known in the art, typically employing a gas-driven infusion principle. U.S. Pat. Nos. 5,318,557 and 5,527,288 describe an inexpensive, gas-driven infusion device which can be manufactured sufficiently inexpensively in order to constitute a disposable product. The embodiments described therein employ an electrolytic cell for gas production as per U.S. Pat. No. 5,062,834. A similar gas-driven device is described in U.S. Pat. No. 5,354,264. This device utilizes gas pressure from free oxygen and hydrogen derived from the electrolysis of water at the electrodes in negatively charged polymeric hydrogels. Said device ensures that the gas generated remains within the walls of the gas chamber by making said walls “rigid and impermeable to gases”. In all these devices, the gas pressure forces the infusion of the drugs through appropriate means into the body, with the pressure being dependent on the rate of electrolysis, which is in turn controlled by an electric current. A further class of devices uses the same gas-driven principle, but generates this gas by chemical rather than electrical means. For example, U.S. Pat. No. 5,814,020, hereby incorporated by reference, describes a gas-powered infusion device where the gas is generated either by an electrolytic cell or by the reaction between citric acid and sodium bicarbonate; said reaction generating carbon dioxide and water.
The central problem with these gas-driven devices is that they all employ a gas-filled chamber in order to drive the drug infusion. As gases are very susceptible to changes in ambient temperature and air pressure, the danger of employing this principle is that a significant and undesirable change in the flow-rate will occur as such temperature or pressure changes occur. For example, a loss of pressure in an airplane could result in a sudden bolus being delivered at an inappropriate time. Similarly, a drop in temperature could result in the drug infusion stopping. For these reasons, despite massive development efforts, these products have faced considerable commercial obstacles to implementation. The prior art confirms the problematic nature of this issue: In a partial attempt to address this issue, U.S. Pat. No. 6,186,982 describes a flow-regulation chamber appropriate to the above-described devices which attempts to compensate for such temperature and/or pressure changes. Nonetheless, this issue of heat and pressure sensitivity is an inherent disadvantage inhibiting the commercialization of these products. Additionally, even when the surrounding conditions are constant, these technologies suffer from the disadvantage of providing a time-lagged response to the control system. For example, if the system's control requires a complete halt of the drug delivery, the residual gas pressure will keep pushing the drug out.
Further prior art in this field includes (a) MEMS-based pumps in which a miniature pump is implemented on a silicon chip using integrated-circuit fabrication techniques, such as the Chronojet™ from Debiotech S. A. (Lausanne, Switzerland); (b) those in which a piezo-electric pumping mechanism is used such as U.S. Pat. No. 6,589,229; and (c) those which use SME wire technology such as the OmniPod™ product from Insulet, Inc. (Bedford, Mass., USA). All these approaches entail complicated mass-manufacturing issues, which have either not yet been solved or require elaborate control mechanisms and fine tolerances; both of which greatly increase costs to the point where it is difficult to produce a disposable product.
Another major concern with existing drug delivery devices is the difficulty of making such a complex mechanism (and its associated electronics) waterproof. This issue is tackled either by the users being very careful not to get it wet, or by a complex sealing of the the mechanism package. Said sealing is inherently difficult with permanent pump devices where new disposable infusion sets need to be periodically attached to the device.
Accordingly, there is a need for an inexpensive drug-delivery device which is capable of very precise actions while only requiring low manufacturing tolerances, and is simple to operate with minimal requirements for internal control/feedback mechanisms.
It is also the object of the present invention to provide a drug-delivery device which is relatively insensitive to temperature and pressure changes.
It is a further object of the invention to provide a drug-delivery device where an electrochemical cell provides the main power source for said delivery.
It is a still further object of this invention to provide a drug-delivery device with a minimum of moving parts.
It is a still further object of this invention to provide a drug-delivery device with inherent position determination.
It is a still further object of this invention to provide a drug-delivery device which does not suffer from a lag in response time.
It is a still further object of this invention to provide a drug-delivery device which is inherently waterproof.
It is still further object of the present invention to provide a drug-delivery device where control and maintenance issues are simpler than in existing approaches and with less potential failure modes.
These and other objects of this invention will become more evident in the summary of the invention and in the description of the preferred embodiment.